Practical Work In Geography Part I Chapter 3 Graphical Representation Of Data

C.

Dot maps

A.

Line graph

C.

More than two variables

D.

Flow map

Thematic maps are the maps which are drawn to understand the patterns of the regional distributions or the characteristics of variations over space.

Bar diagram: The bar diagrams are drawn through columns of equal width. It is also called a column diagram.

Compound bar diagram: When different components are grouped in one set of variable or different variables of one component are put together, their representation is made by a compound bar diagram. In this method different variables are shown in the single bar with different rectangles.

Requirements:

1. An administrative map of the given area showing state/district/block boundaries.

2. Statistical data on selected theme for the choosen administrative units i.e., total population growth, etc.

3. Selection of a scale to determine the value of a dot.

4. Physiographic map of region especially relief and drainage maps.

A traffic flow map can be drawn on some basis. The following requirements are necessary:

1. A route map depicting the desired transport routes along with the connecting stations.

2. The data pertaining to the flow of goods number of the vehicles etc., along with the point of origin and destination of the movements.

3. The selection of a scale through which the data related to the quantity passengers and goods or the number of vehicles is to be represented.

An imaginary line which joins the places of equal values is referred as isopleth. These include isotherms, isobars, isohytes, isonephs, isohets, contours etc.

Interpolation is carried out in the following method:

1. Firstly determine the minimum and maximum values given on the map.

2. Calculating the range of value.

3. Based on range determine the interval in a whole number like 5, 10, 15, etc.

4. The exact point of drawing an isopleth is determined by using following formula :

The following steps are to be followed in preparing a choropleth map:

1. Arrange the data in ascending or descending order.

2. Group the data in five categories to represent very high, high, medium, low and very low.

3. The interval between the categories may be identified on the following formula i.e., range/ 5 and range = Maximum value-Minimum value.

4. Patterns, shades or color to be used to depict the choosen categories should be marked in an increasing or decreasing order.

Important steps:

1. Arrange the data in an ascending order.

2. Calculate the degrees of angles showing the given values.

3. Plot the data dividing the circle into the required number of divisions.

4. Select a suitable radius for the circle to be drawn.

5. Draw a line from the centre of the circle to the arc as a radius.

6. Measure the angles from the arc of the circle for each category of vehicle in an ascending order clockwise starting with smaller angle.

Do yourself.

Do Yourself.

Salient Feature of a flow map: Flow map convey the idea of movement. Hence they are constructed to show movement or flow of buses, trains and other means of transport. They also show the flow of water in the rivers and movement of men and material. The following two features are important in a flow map :

1. The direction of flow.

2. Number or quantity of vehicles, people, commodities etc. from a place to another.

3. A map of the selected area showing transport routes and important places is drawn.

4. Datas to be shown on map are compiled.

5. A suitable scale is selected to represent the number or quantity by thickness of the line proportionate to the number or quantity to be shown.

Tips: -

V. Imp.

The following points should be considered before constructing a dot map:

1. Determine the Value of Dot: It depends upon (a) Scale of the map (b) Range of data (c) The type of element to be shown.

2. Size of Dots: The size of the dot, should neither bo so large that the entire map looks overcrowded nor it should be so small that even the areas of high concentration look empty.

3. Spacing or Placing the Dots: As a rule dots are placed exactly according to the actual distribution of the concerned element. The number of dots is large in areas of high concentration while lesser dots may be put in areas of low concentration. No dots are placed over negative areas like water bodies, marshes, rugged and forested areas.

4. Uniformity of Dots: All the dots placed on the map should be of uniform size and they should be uniformly round in shape.

Tips: -

M. Imp.

The choropleth map is used when data are given in the form of per unit area, average figures or percentage values i.e. density of population, proportion of cultivated land to total land, ratio of irrigated land to cultivated land etc. In other words, the maximum use of this method is made in Human Geography.

Merits of Dot Method:

1. This method is better than any other methods of showing distribution because of its accuracy. The distribution of dots is similar to the commodity shown by them.

2. This is the best method for showing the absolute figures.

3. It provides a better visual effect and is more useful than the other methods of showing distribution.

4. We can have an idea of the figures shown on the map by counting the dots.

5. A dot map can be converted into choropleth or isopleth map but choropleth and isopleth maps can not be trasferred into a dot map.

6. We do not have to look at the index time and again (as in case of choropleth maps) the dots maps can be easily read.

7. More than one element can be shown on a single map by using multiple dot method.

Demerits of Dot Method:

1. It requires a good deal of practice to draw dot maps.

2. This is useful for absolute figures only. Relative figures such as density of population, proportion of agricultural land to total land etc. cannot be shown by dot method.

3. The dot method loses much of its significance if the data are not available for small divisions of area.

4. In addition to the base map with administrative boundaries, we need maps showing relief, climate, soils, vegetation, water-bodies etc. for preparing a dot map. These maps are often not readily available.

5. It is almost impossible to draw a perfect dot map in the absence of complete geographical knowledge of the area and knowledge of the element to be shown.

6. A dot on the map covers 2 to 5 times the actual area on the ground. This gives erroneous picture of the distributional pattern. This exaggeration is about hundred times in case of small and very small maps which further adds to distortion.

7. It is difficult to detect the errors made by the cartographer in placing the dots on a dot map.

Merits of Shading Method:

1. This is a simple method which gives comparative distribution at a glance.

2. This method is very useful for representing relative data, e.g., density of population, sex-ratio, percentatge increase in population, proportion of urban or rural population to total population, percentage of cultivated land to total land, percentage area under wheat to total cultivated areas, etc.

3. Shading method is especially suited to those elements in which there is abrupt change, for example density of population.

Demerits of Shading Method:

1. In this method, we have to follow the administrative divisions whereas most of geographical elements change according to natural divisions. This leads to misunderstanding.

2. There seems to be abrupt change in the density or intensity when we move from one shade to the other whereas, in nature, these changes are slow and gradual.

3. The extreme value of class-interval are shown by the same shade which is misleading.

4. The other details are hidden by the shades and are not shown separately.

Merits of Isopleth Technique.

1. This is a very effective method of showing distribution and variation.

2. It is ideally suited for showing climatic elements, gradient and transitional belt.

3. Isotherms, isobars and isohyets are important examples of this method.

4. Isopleths do not follow administrative boundaries and show the elements in their natural form.

Demerits of Isopleth Technique :

1. Isopleths normally show natural elements whereas data are often available according to administrative units.

2. Many isopleths are drawn by interpolation which sometimes lead to inaccuracy in the directions of isopleths and the pattern of distribution shown by those lines is distorted.

3. The isopleths lose their significance, whenever there is abrupt change in density or intensity.

4. When transitional belts are not wide enough, these lines lose their importance.

Some of the general rules for constructing diagrams are as follows:

1. Attractive and effective: The diagram must be attractive and effective in communicating the required information.

2. Title: Diagrams must bear proper headings. A heading must be simple, short and informative.

3. Proper Size: Diagrams must suit the size of the paper, it should be neither too big, nor too small.

4. Proper Scale: Before making a diagram its scale should be properly determined and indicated as well.

5. Use of signs and colours: Diagrams must carry some signs on the nature and classification of information. Colours may be used to indicate different aspects of diagram.

6. Less use of words or numericals: In diagrammatic presentation of data one should make use of minimum number of words and calculations.

7. Footnote and Index: In case any feature of the diagram has not been adequately made clear footnote should be given. Different types of lines or shades should be given so that the reader can easily understand the diagram.

8. Simplicity: Diagrams should be simple as far as possible so that the reader can understand them clearly.

The suitable diagram will be Pie Diagram. Before constructing Pie Diagram decide the angles for each item. Table:

The same is done in the form of a table.

Tips: -

Imp.

Construction: Select the suitable interval keeping the maximum and minimum density of population. The interval is given below : 175,175-250, 251-325, 326-400 above 401.

Now select the shade according to increasing population.

Since the data are available according to districts, we must have an outline map of Haryana on which boundaries of all the 19 districts are drawn. Taking into consideration the size of the districts and their population figures, fix the value of each dot. Supposing each dot represents a population of 20,000. The number of dots to be put in each district is calculated by dividing total population by the fixed value of dot. The calculation of number of dots in each district is done according to the following table. If the number of dots is in decimals or fractions, they are to be converted into whole numbers.

Calculate the number of dots required for each district when each dot represents 20,000 persons. For example, the dots for Faridabad district will be 219376 % 20,000 = 109.66 round to 110 dots. Similarly calculate the number of dots for each district. On the outline map of Haryana mark the towns and cities and negative areas with pencil. Put more dots near towns and cities and leave out negative areas. Size of the dots should be suitably selected, so that they don't look either too crowded or too sparsely distributed. The size of the dots should remain the same at every spot.

Method of Construction:

Isopleths are drawn on the map when point data are available. Fix the relative positions of maximum points on the map and put their values.

Let us suppose that we are given the location of several points along with their temperature in °C, on an imaginary map as shown in Fig. The minimum value is 4°C and the maximum value is 26°C. Suppose we have to draw isotherms at 5°C interval. The isotherm of minimum value will be of 5°C while that of maximum value will be of 25°C. Two points of 5°C temperature are already given of the map. We can find out the position of the third point having 5°C temperature by method of interpolation. For this purpose join point A of 10°C temperature with point B of 4°C temperature. Divide the line AB into 10 - 4 = 6 equal parts and locate the point having 5°C temperature by counting five divisions from A or one division from B. Join all the three points having 5°C temperature by a curved line. This line will be the isotherm of 5°C. Similarly, interpolate the points of 10°C temperature between C and D, and 15°C temperature between E and F and G and H and complete the isotherms of 10°C and 15°C respectively. Draw the rest of the isotherms in a similar manner and complete the map as shown in Fig.

Sometimes, the space between isopleths is shaded or coloured whose intensity increases with the increase in value. This brings in more clarity of the distribution. At times, tints of the same colour are also used.

Isopleths are used to show the following :

1. Climatic elements and relief features.

2. Density of population.

3. Distribution of crops.

Care should be taken to convert the data into ratios, percentages or index of concentration before actually plotting them on the map. For example, if we want to show the density of population in India, the density for each district will have to be calculated by dividing the population by its area. This will facilitate the drawing of isopleths. Similarly area under a particular crop is shown as percentage of the total cropped area.

It is very simple to construct and can easily be read. It covers less space as compared to other diagrams.

The diagrams which represent statistical data are known as statistical diagrams.

The other names of pie diagram are wheel diagram, Coin diagram and Divided circle diagram.

A combined line and bar graph can show two elements such as temperature and rainfall simultaneously.

It is special type of bar which is subdivided into a number of divisions and shows the total value as well as the values of compound of the total value.

This is simple graph in which the statistical data are shown with the help of a line.

There are several types of diagrams:

1. Line graph, 2. Bar diagram, 3. Combined line and bar graph, 4. Pie or wheel diagram, 5. Flow diagram, 6. Star diagram.

An isopleth is a line joining places of equal value.

1. Qualitative distribution maps.

2. Quantitative distribution maps.

Wind rose is the common example of star diagram.

The greatest handicap in drawing flow diagram is the non-availability of the concerned data.

The minimum number of commuters is 2000 and maximum number is 30,000. Select a suitable scale and ribands showing the number of commuters on each road.

The thickness of the ribands should be in proportion to the number of commuters.